Long noncoding RNA (lncRNA) is an emerging category of transcript, and comprises the majority of the transcriptome of various complex organisms. The biological functions of only a handful of lncRNAs have been investigated in detail, showing involvement in a wide range of biological processes through different functional paradigms. However, most lncRNAs remain to be identified. Many lncRNAs are predicted to function, often preferentially, in the nervous system, potentially playing roles in mediating neural functions such as development, behavior, and cognition. To examine the biological significance and potential mechanisms of the remaining unknown neural lncRNAs, certain tractable model organisms, such as Drosophila, can provide advantages including the use of numerous genetic tools. Herein, we summarize recent progress on the in vivo or potential functions of Drosophila lncRNAs, in particular, behavior and development-related lncRNAs.

Drosophila melanogaster feeds mainly on rotten fruits, which contain many kinds of sugar. Thus, the sense of sweet taste has evolved to serve as a dominant regulator and driver of feeding behavior. Although several sugar receptors have been described, it remains poorly understood how the sensory input is transformed into an appetitive behavior. Here, we used a neural silencing approach to screen brain circuits, and identified neurons labeled by three Gal4 lines that modulate Drosophila feeding behavior. These three Gal4 lines labeled neurons mainly in the suboesophageal ganglia (SOG), which is considered to be the fly’s primary taste center. When we blocked the activity of these neurons, flies decreased their sugar consumption significantly. In contrast, activation of these neurons resulted in enhanced feeding behavior and increased food consumption not only towards sugar, but to an array of food sources. Moreover, upon neuronal activation, the flies demonstrated feeding behavior even in the absence of food, which suggests that neuronal activation can replace food as a stimulus for feeding behavior. These findings indicate that these Gal4-labeled neurons, which function downstream of sensory neurons and regulate feeding behavior towards different food sources is necessary in Drosophila feeding control.

The fruit fly, Drosophila melanogaster, is able to discriminate visual landmarks and form visual long-term memory in a flight simulator. Studies focused on the molecular mechanism of long-term memory have shown that memory formation requires mRNA transcription and protein synthesis. However, little is known about the molecular mechanisms underlying the visual learning paradigm. The present study demonstrated that both spaced training procedure (STP) and consecutive training procedure (CTP) would induce long-term memory at 12 hour after training, and STP caused significantly higher 12-h memory scores compared with CTP. Label-free quantification of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and microarray were utilized to analyze proteomic and transcriptomic differences between the STP and CTP groups. Proteomic analysis revealed 30 up-regulated and 27 down-regulated proteins; Transcriptomic analysis revealed 145 up-regulated and 129 down-regulated genes. Among them, five candidate genes were verified by quantitative PCR, which revealed results similar to microarray. These results provide insight into the molecular components influencing visual long-term memory and facilitate further studies on the roles of identified genes in memory formation.

The fan-shaped body is the largest substructure of the central complex in Drosophila melanogaster. Two groups of large-field neurons that innervate the fan-shaped body, viz., F1 and F5 neurons, have recently been found to be involved in visual pattern memory for “contour orientation” and “elevation” in a rut-dependent manner. The F5 neurons have been found to be responsible for the parameter “elevation” in a for-dependent manner. We have shown here that the F1 neuron also affects visual memory for “contour orientation” in a for-dependent way. With the help of Gal4/UAS and FLP-out techniques, we have characterized the morphological features of these two groups of neurons at single neuron resolution. We have observed that F1 or F5 neurons are groups of isomorphic individual neurons. Single F1 neurons have three main arborization regions: one in the first layer of the fan-shaped body, one in the ventral body, and another in the inferior medial protocerebrum. Single F5 neurons have two arborization regions: one in the fifth layer of the fan-shaped body and the other in the superior medial protocerebrum. The polarity of the F1 and F5 neurons has been studied with the Syt-GFP marker. Our results indicate the existence of presynaptic sites of both F1 and F5 neurons located in the fan-shaped body and postsynaptic sites outside of the fan-shaped body.

•Wild-type and two mutant esterases from two insects are transferred to fruit flies.•G/A151D or W271L mutation disrupts enzyme's original activities.•Mutant esterases bring at most low organophosphate resistance in flies.•Overexpression of any type of esterases causes low insecticide resistance.Carboxylesterases are mainly involved in the mediation of metabolic resistance of many insects to organophosphate (OP) insecticides. Carboxylesterases underwent two divergent evolutionary events: (1) quantitative mechanism characterized by the overproduction of carboxylesterase protein; and (2) qualitative mechanism caused by changes in enzymatic properties because of mutation from glycine/alanine to aspartate at the 151 site (G/A151D) or from tryptophan to leucine at the 271 site (W271L), following the numbering of Drosophila melanogaster AChE. Qualitative mechanism has been observed in few species. However, whether this carboxylesterase mutation mechanism is prevalent in insects remains unclear. In this study, wild-type, G/A151D and W271L mutant carboxylesterases from Culex pipiens and Aphis gossypii were subjected to germline transformation and then transferred to D. melanogaster. These germlines were ubiquitously expressed as induced by tub-Gal4. In carboxylesterase activity assay, the introduced mutant carboxylesterase did not enhance the overall carboxylesterase activity of flies. This result indicated that G/A151D or W271L mutation disrupted the original activities of the enzyme. Less than 1.5-fold OP resistance was only observed in flies expressing A. gossypii mutant carboxylesterases compared with those expressing A. gossypii wild-type carboxylesterase. However, transgenic flies universally showed low resistance to OP insecticides compared with non-transgenic flies. The flies expressing A. gossypii W271L mutant esterase exhibited 1.5-fold resistance to deltamethrin, a pyrethroid insecticide compared with non-transgenic flies. The present transgenic Drosophila system potentially showed that a quantitative increase in carboxylesterases induced broader resistance of insects to insecticides than a qualitative change.Download high-res image (60KB)Download full-size image

Nitric oxide (NO) plays an important role in learning and memory which is essential for animals to adapt to the external environment. However, little is known about the role of NO metabolism in this process. S-nitrosoglutathione reductase (GSNOR) is a key protein in the control of NO metabolism and protein S-nitrosation. To study the relationship between NO metabolism and learning and memory, the expression of gene fdh which is homolog to mammalian GSNOR was modulated by the Gal4/UAS system in Drosophila. The over-expression of the fdh in the central nervous system significantly increased GSNOR activity and induced visual pattern memory defects of Drosophila. The role of fdh in learning and memory was independent of development and was neuron-specific: over-expression of the fdh in the fan-shaped body induced memory defect, while over-expression in the mushroom body did not. The visual pattern memory defect could be rescued by co-expression with exogenous cGMP-dependent protein kinase (PKG). Moreover, fdh over-expression resulted in denitrosation of multiple proteins functionally enriched in vesicle-mediated transport, which is important for learning and memory. These results showed that regulation of NO metabolism plays an important role in learning and memory, and the mechanism may involve both NO-cGMP-PKG signaling pathway and S-nitrosation modification.